Self-attaching female fasteners, including pierce nuts, generally include a central projecting pilot portion having a planar end face, a bore extending through the end face which may be threaded or unthreaded, flange portions on at least opposed sides of the pilot portion each having a planar bearing face spaced below the plane of the end face of the pilot portion, and grooves in the bearing face of the flange portion or in the sides of the pilot portion which receive the panel and retains the self-attaching female fastener element on the panel.
Self-attaching female fastener elements of the type described above may be formed by either rolling a metal wire into the desired shape, cutting the wire to the desired length and piercing a bore, wherein the fastener is rectangular, or formed by cold header techniques, wherein the nut is generally annular or cylindrical, and the flange portion and the groove surround the pilot portion. The self-attaching female fastener elements formed by each of these methods has certain advantages. For example, a rectangular pierce nut formed by rolling generally has superior retention, including push-off strength and resistance to rotation in the panel compared to a round or cylindrical nut formed by cold heading. However, rolling techniques used for manufacturing self-piercing nuts require a rolling mill, expensive equipment and know how. Further, a pierce nut having a rectangular pilot may form stress risers in the panel adjacent the corners of the pilot during installation. A self-attaching nut, particularly a pierce nut, formed by conventional cold header techniques is less expensive to manufacture, but generally has less structural integrity in the joint, particularly including torque resistance or resistance to rotation of the nut in the panel after installation. It is therefore a primary object of this invention to provide a self-attaching female fastener element, particularly including a pierce nut, which may be formed by conventional cold header techniques, and which provides improved structural integrity when installed in a panel, including improved push-off strength and resistance to rotation of the nut on a panel compared to conventional pierce nuts formed by cold heading techniques.
U.S. Pat. No. 5,531,552, assigned to the predecessor in interest of the assignee of this application, discloses a self-attaching female fastener element, which may be utilized as a pierce nut, formed by conventional cold header techniques. However, pierce nuts formed by the method disclosed in this patent when installed in a panel do not have sufficient structural integrity for many applications, particularly including relatively thin metal panels as used by the automotive and appliance industries. It is therefore a further object of this invention to improve the push-off strength and torque resistance of the fastener disclosed in this patent.